This project I will develop the pathology techniques necessary for the proper performance of the new multicenter trial of intraoperative lymphatic mapping and sentinel lymph node dissection (MSLT-II), described in Project 0001. These activities will include development of guidelines for analysis of all tissue samples, creation of instructional materials, and the design and implementation of centralized and on-site training for personnel at participating institutions. Primary melanoma and sentinel node specimens from this trial will be analyzed to assure quality and to assess specific features that may predict the tumor status of nonsentinel nodes and the patient's clinical outcome. These activities will focus on the amount of tumor in the sentinel node, the characteristics of these tumor cells, and the immune competence of the sentinel node. These observations will be compared and correlated with molecular pathology observations from Project 0003. This project has four specific aims: 1. To provide accurate and uniform pathologic interpretation of primary tumors and node-metastatic melanomas affecting potential participants in MSLT-II. 2. To assess the capacity of pathologic features of the primary melanoma and the sentinel node to predict the likelihood that additional metastatic tumor will be present in nonsentinel nodes. 3. To determine the nature and significance of morphological changes indicative of immune modulation of the sentinel node. 4. To compare the predictive accuracy for recurrence and survival of the combined factors assessed above by anatomic pathology-related approaches.